Method of copper/copper surface bonding using a conducting polymer for application in IC chip bonding

ABSTRACT

A semiconductor chip having an exposed metal terminating pad thereover, and a separate substrate having a corresponding exposed metal bump thereover are provided. A conducting polymer plug is formed over the exposed metal terminating pad. A conforming interface layer is formed over the conducting polymer plug. The conducting polymer plug of the semiconductor chip is aligned with the corresponding metal bump. The conforming interface layer over the conducting polymer plug is mated with the corresponding metal bump. The conforming interface layer is thermally decomposed, adhering and permanently attaching the conducting polymer plug with the corresponding metal bump. Methods of forming and patterning a nickel carbonyl layer are also disclosed.

This is a division of patent application Ser. No. 10/076,244, filingdate Feb. 13, 2002, now U.S. Pat. No. 6,821,888 A Method OfCopper/Copper Surface Bonding Using A Conducting Polymer For ApplicationIn IC Chip Bonding, which is a Continuation-In-Part of patentapplication Ser. No. 09/612,576, filing date Jul. 7, 2000, nowabandoned, A Method Of Copper/Copper Surface Bonding Using A ConductingPolymer For Application In IC Chip Bonding, now abandoned, assigned tothe same assignee as the present invention, which are hereinincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the packaging ofsemiconductor devices, and more specifically to copper interconnectprocesses between chips and substrates in packaging processes.

BACKGROUND OF THE INVENTION

Recent integration of copper interconnect processes into IC (integratedcircuit) manufacturing requires copper terminating chips to be bondeddirectly on the copper metal pad and circuit boards. The presentinvention allows the use of conducting polymers to bond copperterminating chips directly on copper substrate or printed circuitboards.

U.S. Pat. No. 5,923,955 to Wong describes a process for creating aflip-chip bonded combination for a first and second integrated circuitsusing a Ni/Cu/TiN structure.

U.S. Pat. No. 5,891,756 to Erickson describes a method for forming asolder bump pad, and specifically to converting a wire bond pad of asurface-mount IC device to a flip-chip solder bump pad such that the ICdevice can be flip-chip mounted to a substrate. The method uses a Nilayer over the pad.

U.S. Pat. No. 5,795,818 to Marrs describes a method of forming aninterconnection between bonding pads on an integrated circuit chip andcorresponding bonding contacts on a substrate. The method uses coinedball bond bumps.

U.S. Pat. No. 5,904,859 to Degani describes a method for applying underbump metallization (UBM) for solder bump interconnections oninterconnection substrates. The UBM comprises a Cu, Cu/Cr, Cr multilayerstructure.

U.S. Pat. No. 5,767,009 to Yoshida et al. describes a method of reducingcross talk noise between stacked semiconductor chips by the use of achip on chip mounting structure.

U.S. Pat. No. 5,804,876 to Lake et al. describes a low contactresistance electrical bonding interconnect having a metal bond padportion and conductive epoxy portion.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention is to provide amethod of bonding a chip to a substrate without the need for a bumpmetal, wetting agents, and barrier materials.

Another object of the present invention is to provide a method ofbonding a chip to a substrate avoiding the use of environmentallyunfriendly solder and solder material.

An additional object of the present invention is to provide a method ofbonding a chip to a substrate in smaller micron scale metal pitch sizes.

Other objects will appear hereinafter.

It has now been discovered that the above and other objects of thepresent invention may be accomplished in the following manner.Specifically, a semiconductor chip having an exposed metal terminatingpad thereover, and a separate substrate having a corresponding exposedmetal bump thereover are provided. A conducting polymer plug is formedover the exposed metal terminating pad. A conforming interface layer isformed over the conducting polymer plug. The conducting polymer plug ofthe semiconductor chip is aligned with the corresponding metal bump. Theconforming interface layer over the conducting polymer plug is matedwith the corresponding metal bump. The conforming interface layer isthermally decomposed, adhering and permanently attaching the conductingpolymer plug of the semiconductor chip with the corresponding metal bumpof the separate substrate. Methods of forming and patterning a nickelcarbonyl layer are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be moreclearly understood from the following description taken in conjunctionwith the accompanying drawings in which like reference numeralsdesignate similar or corresponding elements, regions and portions and inwhich:

FIGS. 1 to 6 schematically illustrate in cross-sectional representationa preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Unless otherwise specified, all structures, layers, etc. may be formedor accomplished by conventional methods known in the prior art.

Accordingly, as shown in FIG. 1, semiconductor structure 200 includes anoverlying final metal layer 212 connected to, for example, metal line214 through metal via 216. Metal terminating pad 218 overlies finalmetal layer 212 at a predetermined position within first passivationlayer 220.

Semiconductor structure 200 is understood to possibly include asemiconductor wafer or substrate, active and passive devices formedwithin the wafer, conductive layers and dielectric layers (e.g.,inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed overthe wafer surface. The term “semiconductor structure 200” is meant toinclude a semiconductor chip.

Final metal layer 212 and metal terminating pad 218 are preferablycomprised of copper as will be used for illustrative purposes hereafter.

Additional metal vias 216, metal lines 214, metal terminating pads 218,etc., may be formed within and over semiconductor structure 200 althoughfor purposes of illustration, only single such structures are shown inFIG. 11. For purposes of simplicity, metal via 216, metal line 214, andfinal metal layer 212 are not explicitly illustrated in the followingFIGS. 2–6.

Final passivation layer 222 is formed over first passivation layer 220and copper terminating pad 218 to a thickness of from about 1000 to10,000 Å, and more preferably from about 2000 to 5000 Å.

Opening 224 is formed within second passivation layer 222 exposingcopper terminating pad 218.

As shown in FIG. 2, planarized conducting polymer plug 250 is formedwithin opening 224 by flowing or using a spin-on-technique on coppersurfaces such a bonding pads 218 or copper tracks on printed circuitboards. Planarized conducting polymer plug 250 is preferably from about1000 to 10,000 Å thick, and more preferably from about 3000 to 6000 Åthick.

Conducting polymer plug 250 includes, but is not restricted to dopedpolyacetylene, poly(para-phenylene vinylene) (PPV), or polyanilinemanufactured by DuPont, Ciba Geigy, and Sieman's and others.

Conducting polymer plug 250 is used to achieve an effectivecopper/copper surface bonding in copper terminating IC chip pads 218.The conducting polymer has good conductive properties, is highly dopedto degeneracy (see below), has good adhesive properties and very usefulthermal insulation properties.

The main characteristics of the conducting polymer forming conductingpolymer plug 250 is the presence of the so-called conjugated chain wherethe chemical bonding between the atoms in the mainly carbon “backbone”of the polymer chain alternates between single and double bonds.

There are two types of bonds namely the omega-bond and the phi-bond.Electrons in the former (omega-bond) are strongly localized and formstrong bonds, in contrast to the later (phi-bond) in which the electronsform weak bonds and are not localized.

The electrons in phi-bonds can be thought of a cloud that extends alongthe entire length of the conjugated chain in which electrons are free tomove in a similar fashion to conducting electrons in a metal. Theconducting polymer is heavily doped to achieve a conduction which iscomparable to a degenerate semiconductor and is sufficient enough not toperturb the device performance.

As shown in FIG. 3, interface layer 260 is formed over secondpassivation layer 222 and conducting polymer plug 250. Interface layer260 is preferably comprised of nickel carbonyl (Ni(CO)₄) as will be usedfor illustrative purposes hereafter. The material for interface layer isselected to be subject to thermal decomposition be chemical combustible.

Ni(CO)₄ has a freezing point of −19° C., between −19° C. and 40° C.nickel carbonyl exists as a liquid and, at temperatures above 40° C.,the following reaction takes place:Ni(CO)₄→Ni+4COBelow 40° C., the reverse reaction takes place:Ni+4CO→Ni(CO)₄

Two methods may be used to form Ni(CO)₄ interface layer 260. In thefirst method, nickel is first deposited (through sputtering orelectroplating) over second passivation layer 222 and conducting polymerplug 250. Then, carbon monoxide (CO) is introduced into the reactionchamber and reacts with the deposited nickel layer to form Ni(CO)₄interface layer 260. The CO may be pressurized as necessary. Thetemperature of the chamber and/or the temperature of the wafer must beless than 40° C. to form the Ni(CO)₄ and then keep below −19° C. tomaintain the Ni(CO)₄ interface layer 260 as a solid.

In the second method, liquid Ni(CO)₄ (at a temperature between −19° C.and 40° C.) is flowed over second passivation layer 222 and conductingpolymer plug 250 and then the temperature of the chamber and/or thetemperature of the wafer is lowered to less than −19° C. so as toconvert the liquid Ni(CO)₄ into solid Ni(CO)₄ interface layer 260.

Regardless of which method is used, the temperature of the chamberand/or the temperature of the wafer must be less than −19° C. tomaintain the Ni(CO)₄ interface layer 260 as a solid.

As shown in FIG. 4, the excess of Ni(CO)₄ interface layer 260 not overconducting polymer plug 250 is removed to form conforming Ni(CO)₄interface layer 260′ over conducting polymer plug 250. To remove theexcess of Ni(CO)₄ interface layer 260 not over conducting polymer plug250, a partial chrome photomask (not shown) is formed over the waferwith the chrome portion of the photomask overlying that portion of theNi(CO)₄ interface layer 260 overlying the conducting polymer plug 250.The partial chrome photomask is then subjected to a radiation sourcesuch that radiation penetrates the photomask to the Ni(CO)₄ interfacelayer 260 not over conducting polymer plug 250 and raising thetemperature of that portion of the Ni(CO)₄ interface layer 260 above 40°C. so that the reactionNi(CO)₄→Ni+4COtakes place, removing the Ni(CO)₄ interface layer 260 not overconducting polymer plug 250. No radiation may penetrate the chromeportion of the photomask overlying the Ni(CO)₄ interface layer 260 overconducting polymer plug 250 so that portion of the Ni(CO)₄ interfacelayer 260 remains as Ni(CO)₄.

Final passivation layer 222 is also then removed, exposing conductingpolymer plug 250 with overlying conforming Ni(CO)₄ interface layer 260′.As shown in FIG. 5, pre-formed metal bump 300 (connected to metal track310 within substrate 320) is aligned, mechanically pressed, and matedwith, conducting polymer plug 250 with overlying conforming Ni(CO)₄interface layer 260′. Substrate 320 may be a bond pad or a printedcircuit board, for example.

Metal bump 300 and metal track 310 are preferably comprised of copper aswill be used for illustrative purposes hereafter. Cu metal bump 300 isformed by electroless plating, at about 200° C.

As shown in FIG. 6, conforming Ni(CO)₄ interface layer 260′ thermallydecomposes allowing copper bump 300 to adhere directly with conductingpolymer plug 250 at temperature above about 40° C.:Ni(CO)₄→Ni+4COWith slight application of pressure, the thermal decomposition ofNi(CO)₄ interface layer 260′ facilitates Ni bonding of copper bump 300to conducting poly plug 250.

The present invention may find wide application in flip-chip,chip-on-board, and micron metal bonding and provides for micron scalebonding.

Thus, the present invention permits semiconductor chips with copperinterconnect termination to be directly bonded by a flip-chip,chip-on-board, and micron metal bonding processes onto a coppersubstrate or printed circuit board, eliminating the need for a bumpmetal, wetting agent metals and barrier materials with the attendantcostly process steps and materials involved. It further avoids the useof environmentally unfriendly solder and solder materials, and allowsfor use in smaller micron scale metal pitch sizes unlike most of thecurrent bonding techniques.

While particular embodiments of the present invention have beenillustrated and described, it is not intended to limit the invention,except as defined by the following claims.

1. A method of forming a Ni(CO)₄ layer, comprising the steps of:providing a substrate within a reaction chamber; forming a layer ofnickel over the substrate; and introducing CO into the reaction chamberat a temperature of less than 40° C. to cause the reactionNi+4CO→Ni(CO)₄ to occur whereby the Ni(CO)₄ layer is formed.
 2. Themethod of claim 1, wherein the nickel layer is formed by sputtering orelectroplating.
 3. The method of claim 1, wherein the CO introduced intothe reaction chamber is pressurized.
 4. The method of claim 1, whereinthe nickel layer is formed by sputtering or electroplating; and the COintroduced into the reaction chamber is pressurized.
 5. The method ofclaim 1, wherein the formed Ni(CO)₄ layer is maintained below −19° C.whereby the formed Ni(CO)₄ layer is solid.
 6. The method of claim 1,wherein the substrate is a semiconductor substrate.
 7. The method ofclaim 1, wherein the nickel layer is formed by sputtering orelectroplating; the CO introduced into the reaction chamber ispressurized; and substrate is a semiconductor substrate.